The complete nucleotide sequence of wild-type HAV strain HM-175 was determined. The genome is 7478 nucleotides long, followed by a poly A tail, and encodes a polyprotein of 2227 amino acids. On the basis of amino acid homology with other picornaviruses, putative cleavage sites for the polyprotein have been identified. The molecular weights of VP1, VP2, and VP3 predicated from the sequence data agree with those determined by biophysical methods. Proteins 2C and 3D are most homologous with other picornaviruses. HAV shares the putative active enzyme sites on proteins 3C and 3D with other picornaviruses. Comparison of wild-type HM-175 with a cell culture adapted strain (Najarian, PNAS 1985) shows 624 necloetide differences (91.7% identity), but only 34 amino acid differences (98.5% identity). Wild-type HAV HM-175 has been passaged 30 times in primary African green monkey kidney (AGMK) cells. The resultant virus, P30 HM-175, is attenuated for chimpanzees. cDNA clones have been prepared from this latter virus and we are currently characterizing the clones. Comparison of the sequence of P30 with wild-type HM-175 HAV should help to locate regions of the genome responsible for adaptation to cell culture and attenuation.